Liquids such as drug solutions and blood are conventionally supplied to patients using a liquid transfusion line or a blood transfusion line provided with a tube. A connecting structure for a connector for connecting the various tubes which make up the liquid transfusion line or the like is used in such cases as for example, in Japanese Unexamined Patent Application Publication H5-31180, entirely incorporated by reference herein. This medical connecting instrument (connecting structure for a connector) is provided with a male connecting instrument which is connected to the ends of respective tubes which are connected to one another, and a female connecting instrument.
The male connecting instrument comprises a communicating pipe of which the tip end part constitutes the outer wall of a luer taper, and an outer cap which surrounds the communicating pipe. The female connecting instrument comprises a cylindrical body which can be inserted into the outer cap, and the communicating pipe can be fitted therein. Furthermore, a screw protrusion is formed on the inner wall of the outer cap, and a screw protrusion which can engage with the screw protrusion on the outer cap is formed on the outer wall of the female connecting instrument. Consequently, the male connecting instrument and the female connecting instrument can be connected in a state in which the communicating pipe is fitted inside the female connecting instrument by screwing the partner screw protrusions together while twisting the outer cap.